We are slightly behind on the release timeline that is contained in that presentation, but work on NetRexx 4.00 has started.
I invite you all to use NetRexx 3.07 from now on for all production work. Do note that with previous releases (from 2015 on) there is a slight chance of classfile corruption when using the ecj compiler in combination with minor classes. This alone, and the improvements on the RexxIO class are worth the trouble of upgrading. In an existing installation, the only change needed is replacing the jar file and an edit of CLASSPATH.
An updated docker image file will find its way to the docker repository soon. I will signal when it is there.
Please send all feedback to this list so we can quickly react if something needs attention.